A robot used in spinal surgery can now guarantee the positioning of ped-icle screws to within a few microns, thanks to the high levels of machining accuracy achieved on the components used on the hexapod robots made by the Swiss company Micro Precision Systems (MPS).
The company manufactures micro-precision ball bearings and ball-bearing-mounted precision systems for highly specialised applications in many industries, which is why the company relies on machinery that provides high levels of accuracy. Nicola Thibaudeau, MPS’s CEO, says: “For us, micro precision is not just a production feature. We live and breathe it each and every day.”
The company and its 150 employees focus on precision guidance systems for linear and rotary movements that support demanding applications in the watch-making, medical device and optical industries. The range of parts produced includes both ballscrew bearings for linear guidance systems and miniature ball bearings for the watch-making industry. Defining the company’s micro-precision credentials, Nicola Thibaudeau confirms: “With stainless steel or ceramic ball bearings, we are working with diameters from 0.200 to 1.588mm at a roundness precision of 0.08µm and a maximum surface roughness of 0.01µm. In the case of ball-bearing-mounted precision systems, we have an ingenious selection process that means we can achieve play of just 6-12µm between precisely fitting ball bearings and ball tracks.”
The need for such high levels of precision is highlighted by the guidance systems for a robot used in surgery. “The surgeon uses the robot arm to guide a laser beam to the operating site with a high degree of precision. This robot arm features four joints, and the laser can be guided within a tolerance of just 0.5mm with the arm extended; and with our ball bearing systems it can do this successfully and repeatedly. In order for us to achieve such a result, we need capable employees and superior machinery.”
Swiss-built sliders
The immaculately clean machine shop at MPS is full of automatic turning machines from Tornos, which has a UK subsidiary in Coalville (Tel: 01530 513100 – www.tornos.com). Regarding the choice of machines, Jean-François Bilat (head of machining and surface technology) says: “We are fundamentally satisfied with Tornos, which is why we continue to rely on the company. If there is a fault, the service staff are on site within a short time, and any spare parts we need also reach us promptly. This is very important for safeguarding our production. Moreover, we generally work with production runs of between 100 and 50,000 pieces, sometimes even fewer; and because our machine shop allows us to use the same tools on various machines from the same manufacturer, our machining department has a very high degree of flexibility.”
When the machining department needed to expand its capacity, head of machining Eric Pesselier said he had initially decided in favour of a new Tornos Deco. “I then saw the EvoDeco 16 at the last Prodex show in Basel. This new model offered several improvements compared to the Deco 13. Indeed, the design concept of the new machine was so convincing that we opted to buy one. It meets our specifications with regard to swapping the tools around, while programming the control and operating the machine are comparable with the Deco 13. This helps us maintain our ability to rotate our staff; and the fact that we can use bar up to 16mm in diameter opens up new potential for future projects.”
Machine ergonomics
Talking of the EvoDeco 16’s details, Mr Bilat says: “Compared with the Deco 13, the machine’s ergonomics have been significantly enhanced, with improved illumination in the working area making it considerably easier to set up and monitor operations during production. Given our relatively small production runs, this is very import-ant to us. Also, the fact that the control panel is now attached to a rotary arm and can help employees at the machining area with setting up and any other interventions is not only convenient but also makes it considerably easier to work on this machine.”
Meanwhile, Mr Pesselier adds: “Precision has always been our core competence, and this is where the Evo Deco 16 gives us considerable benefits. We very quickly saw that the machine was extremely stable, with ‘running-in’ after a weekend standstill particularly brief. After producing three parts or so, this machine has reached a high level of long-term thermal stability. Even with high-precision turned parts, we achieve a constant precision of ±5µm — and that also applies to large production runs.”
MPS manufactures many parts from chrome steels and titanium, with turned parts varying from 2 to 13mm in diameter and from 2 to 250mm in length. Mr Pesselier says that, because both the main spindle and the counter-spindle on the EvoDeco 16 are directly driven by synchronous motors offering high rates of material removal, and because the machine is particularly stable, he prefers to machine larger components with higher chip volumes on this Tornos lathe. “We were also pleasantly surprised that this machine makes less noise than other automatic turning machines — even under heavy loads.” MPS is certified to ISO: 13485 and has a clean room for putting together assemblies that are used for medical applications. That said, the facility is checked regularly, as Mr Bilat highlights: “We record and analyse our part checks statistically so that we can identify any deviation trends very early on. Furthermore, internal audits ensure that quality is always to our high standards; and even though our customers are located world-wide, they regularly check our operation, especially our production equipment.”